TTTop

Have a 2000 TT Quattro with 58K miles on it. Concerned about temp readings. After only 15 minutes of summer (80 degrees) stop-and-go driving, temp climbs and needle moves one click to the right of middle position, ( one click past 12 o'clock position). shortly thereafter, fans kick in and temp gauge cycles back to 12 o'clock position (needle straight up again). I can run the car at 80 mph for over an hour and the temp gauge stays in the middle position. So my question is, is it normal for temp gauge, and I assume running temp to fluctuate that quickly? Is this a normal occurrence for a 2000 TT Quattro? I am certainly no expert and any help greatly appreciated.

Vegas-roadster

No it is not normal. The gauge should always be straight up. It is impossible to diagnose the problem without knowing the service history. First, has your timing belt, tensioner, water pump etc been replaced in the past 5 years? If not you are driving a time bomb. If the timing belt goes, your TT is totaled. If you still have the original water pump, it has a plastic impeller which is likely falling apart and reduced/blocked your coolant flow. The other likely possibility is that your radiator fan thermostat is going bad. Also, has your engine thermostat been replaced? If it was replaced by a non-OEM, it's opening spec could be wrong.

TTTop

Timing belt, tensioner, water pump all replaced > 24 months ago. Coolant replaced too. So you think it is the Thermostat that's going bad?
Thanks!

JoeKan

Check your temp through the Air-Con system - reads the temp sensors directly. Code 49 for the water temp.

I Experienced something similar. All servicing done in the past 100 miles including new thermo. Fine on the highway. City driving, stop & go at 90+F (30C) the sensors read to 102C then the fans kick in and temps drop to ~90C (center of gauge). The temp gauge is an approximation run through the ECU and shouldn't vary by much. Your temp variation on the gauge seems higher than I've experienced, but could be normal as my needle was wiggling as well. Could be your fans may be late to activate, which could be the sensor or thermo. Read your water temp directly and see what the actual readings are.

JoeKan

Check out this thread:
https://www.ttforum.co.uk/forum/view...?f=2&t=1901247

Vegas-roadster

I'd check the fan thermostat first. Surprised you did not change coolant thermostat when you replaced coolant. If you replace coolant thermostat, I'd also replace the top and bottom hoses if they are original. Again, I'd go with the Audi coolant thermostat. Years ago there were lots of posts about engines running slightly hot due to non-OEM thermostats. In fact, I replaced mine with one from the OEM manufacturer (Whaler) but not Audi and my temp ran slightly hot. Turns out Whaler made a special opening temp for Audi.

J. Patterson

Everyone’s info corresponds with my experience over the years. The temperature gauge is center weighted.. It should read straight up and down at coolant temperatures of 80 C to 100 C. ( as read in block 49 in the HVAC display) with a proper OEM thermostat the HVAC display should stay at about 93C when cruising. With air-conditioning on the low speed fans will always run. Both of them. Hi Speed fans will cycle in and out if temperature rises above 105C. They will also come on at lower coolant temperatures if the car is stationery with AC on. The fans are controlled by temperature sensor in the radiator on the lower left side below the battery. It has been my experience that high-speed fan operation can vary a bit from car to car. Fans can fail to run on low speed but still work on high-speed. This is due to the failure of a resistor in the fan motor. This will cause the engine to run it abnormally high temperatures when the car is stationary. This will also adversely affect air-conditioner operation. Remember that both fans should be running on low speed whenever the air-conditioner is on. Good luck with your investigation. I expect based on your description that you may have a low-speed fan not working. You may also have one of those thermostats that runs about 5° high. I have received those twice with timing belt kits.

Scott Johnson

I was having a similar problem a couple of years ago. I live in Florida and the temp was fine while driving down the road when I slowed at for a stop light the gauge would go up 1 tick. It ended up being the the fans were bad. The would work somewhat until they melted the fuse block on top of the battery.

TTTop

It is the low-speed fan thats not working. Thanks!!